This invention relates generally to fiber-optic gyroscopes (gyros) and particularly to a fiber-optic gyro configuration which reduces bias drift error caused by optical back reflections originating at an integrated optic chip/fiber coil interface.
Conventional integrated optic (IO) fiber-optic gyros feature a configuration which includes light from a suitable light source which is transmitted through a directional coupler and then through a polarizer. A tuneable directional coupler splits the light from the polarizer into clockwise and counterclockwise propagating light beams. The light beams are transmitted a particular distance in an IO chip before being coupled into a fiberoptic coil. Back reflections at the chip/coil interface cause a bias drift error which deteriorates gyro performance.
It has been suggested that the I/O chip which may be, for example, of lithium niobate, be angled at the chip/coil interface to reduce the magnitude of the back reflections. Although the idea of an angled interface has been found to dramatically reduce the magnitude of the back reflections and hence improve the bias drift error resulting therefrom, the fabrication of an angled interface is difficult.
The present invention teaches reducing the aforenoted bias drift error by using an IO chip architecture, whereby the distances over which the clockwise and counterclockwise beams are transmitted differs. In the preferred embodiment of the invention this difference is achieved by bending the waveguide over which one of the clockwise and counterclockwise beams is transmitted.
Thus, it is the object of the present invention to provide an integrated optic fiber-optic gyro wherein the chip architecture uses specifically configured waveguides for reducing back reflections causing bias drift error.